In industrial applications where pipes are installed and used to transport fluids including gases, the pipes are often monitored for defects to maintain process reliability and avoid accidents or failures. For example, the pipe wall thickness can be monitored to detect pipe defects and/or anticipate pipe failures. One technique to monitor the pipe wall thickness is based on magnetic flux leakage (MFL) at the walls. A MFL tool or device can be used for wall thickness measurement (WTM). The MFL tool uses a plurality of electric coils or permanent magnets placed on the pipe walls or in proximity of the walls to generate a magnetic field or flux along a portion of the pipe. The electric coils or permanent magnets may be oriented in a specific direction with respect to the pipe to generate the magnetic field in a desired direction, such as in the axial direction to the pipe. As the pipe wall thickness decreases, a change in the magnetic flux signal can be detected using a sensor in proximity of the pipe. The change in the magnetic flux indicates a possible defect in the pipe.
To monitor the wall thickness around the pipe circumference, a plurality of similar WTM devices can be used. For example, a plurality of sensors mounted on a ring can be used as part of an electromagnetic pipe wall monitoring system to measure changes in the average wall thickness along a portion of the pipe and around its circumference. However, before testing pipes with unknown wall thicknesses, such systems need to generate empirical reference curves for each combination of pipe size, material, and wall thickness. These empirical reference curves represent the detected MFL signal versus the actual wall thickness of the pipe, and are obtained in a laboratory by operating a MFL WTM device on a plurality of pipe samples. A separate empirical reference curve is needed for each combination of pipe material, size, and thickness. A pipe wall thickness generally cannot be obtained without an empirical reference curve for a particular combination of these parameters. To determine an unknown pipe thickness, the pipe's magnetic flux density readings are measured, compared to the empirical reference curves, and the pipe thickness is obtained from the empirical reference curves. Such a procedure is cumbersome, time consuming, and costly.